1. Field of the Invention
The present invention relates to a fastening tool and a fastening bolt for fixing two members without applying a large displacement load to the fastening bolt or a seat surface of the member.
2. Disclosure of the Prior Art
Conventionally, a fastening bolt comprises a rod-like bolt body having a male thread, and a head provided on an end of the bolt body, and the fastening bolt is used in various mechanical elements. A bolt body of the fastening bolt is inserted into a bolt through hole formed in a first member, the bolt body is threadedly engaged with a threaded hole formed in a second member, thereby fixing these two members to each other.
The fastening bolt is used for a shaft coupling as a fastening tool as shown in FIG. 8(a).
In this case, a fastening bolt 501 is used for fastening a fastening body 507 for fixing two shafts 505 in a shaft coupling which connects the two shafts 505 to each other (Japanese Patent Application Laid-open No.2001-295851). The fastening body 507 is provided at its central portion with a shaft hole 571 through which the shaft 505 (other member) is inserted, and is provided with a slot groove 572 in its radial direction. The fastening body 507 is provided at its one end 503 (first member) opposed to the slot groove 572 with a bolt through hole 530, and at its other end 504 (second member) with a threaded hole 540. The fastening bolt 501 is threadedly engaged with the threaded hole 540 through the bolt through hole 530. Therefore, if the fastening bolt 501 is threadedly inserted, a distance of the slot groove 572 is reduced, a diameter of the shaft hole 571 of the fastening body 507 is reduced, and the shafts 505 are fastened and fixed by a surface pressure of the shaft hole 571 caused by the diameter reduction.
When the two members 503 and 504 or the like are to be fixed to each other by means of the fastening bolt 501, the threaded hole 540 provided in the members 504 is not perpendicular to the slot groove 572 but is slightly inclined with respect to the groove in some cases. In such a case, a lower surface corner 522 of the head 520 of the fastening bolt 501 abuts against a seat surface 531 of the member 503 having the bolt through hole 530 in substantially a point-to-point manner, and a large displacement load or bending stress is applied to the seat surface 531 or the fastening bolt 501. Therefore, there is a problem that the fastening force of the fastening bolt 501 is insufficient and the fastened portion is prone to get loose. The head 520 and the bolt body 510 of the fastening bolt 501 are inclined in some cases. In such a case also, there is a problem that the fastening force of the fastening bolt 501 becomes insufficient, and the fastened portion is prone to get loose.
In the case of a shaft coupling 600 shown in FIG. 8(a), as the fastening bolt 501 is threadedly inserted, the opposed ends 503 and 504 of the slot groove 572 of the fastening body 507 are inclined and with this, the seat surface 531 of the one end 503 is also inclined. Therefore, as shown in FIG. 8(b), the lower surface corner 522 of the head 520 of the fastening bolt 501 abuts against the seat surface 531 in substantially a point-to-point manner, and a large displacement load is applied to the fastening bolt 501 and the seat surface 531. Thus, a strong force is required for threadedly inserting the fastening bolt 501, and when the one end 503 which forms the seat surface 531 is thin or when the fastening body 507 is formed of soft material such as aluminum, the seat surface 531 sinks (broken line K in FIG. 8(b)), the fastening of the fastening bolt 501 is weakened, and the fastening force of the shafts 505 becomes insufficient.
Since the lower surface corner 522 of the head of the fastening bolt 501 abuts against the seat surface 531 in substantially a point-to-point manner, large bending stress is applied to the seat surface 531 and the fastening bolt 501. For this reason, if a fastening body 507 vibrates when the shaft coupling rotates, a load caused by the vibration is further applied to the seat surface 531 and the fastening bolt 501 and as a result, a crack V (see FIG. 8(b)) is generated in the seat surface 531 or the fastening of the fastening bolt 501 gets loose.
When two slot grooves are provided at two portions and the fastening body is divided into two pieces and two fastening bolts 501 are used to fasten (FIG. 1 of Japanese Patent Application Laid-open No.2001-295851), it is practically difficult to uniformly fasten the fastening bolts 501, and the same problem is generated.